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This article in JEQ

  1. Vol. 33 No. 4, p. 1562-1567
     
    Received: July 22, 2003
    Published: July, 2004


    * Corresponding author(s): michel.vorenhout@ecology.falw.vu.nl
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doi:10.2134/jeq2004.1562

Automated and Continuous Redox Potential Measurements in Soil

  1. Michel Vorenhout *a,
  2. Harm G. van der Geestc,
  3. Daan van Marumb,
  4. Kees Wattelb and
  5. Herman J. P. Eijsackersa
  1. a Institute of Ecological Science, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
    c Aquatic Ecology and Ecotoxicology, Faculty of Science, University of Amsterdam, Kruislaan 320, 1098 SM, Amsterdam, the Netherlands
    b Electronics Department, Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands

Abstract

Redox potential (Eh) describes the electrical state of a matrix. In soils, Eh is an important parameter controlling the persistence of many organic and inorganic compounds. A popular, but also criticized, manual measuring method makes use of a small tip of Pt placed on a copper wire that is placed in the soil; a reference electrode is placed in the same soil at a fixed distance. Fluctuations in redox potential values measured in the soil can be very large and depth-dependent. This will be overlooked when making single-point measurements. We developed the datalogger Hypnos 2.0 for continuous redox potential and temperature measurements at various depths in the soil and without disturbance of the site. Hypnos is field-deployable, relatively cheap, and runs on batteries. The datalogger can use a “sleep mode” between sampling events. In sleep mode, there is no constant voltage on the Pt wire or the reference electrode, but there is only a short pulse during sampling. We did not measure an effect of this short pulse on the measured redox potential. In sandy soils in mesocosms and in a salt marsh soil we measured changes in the Eh as large as from −400 to +100 mV within 4 d, and daily cycles of 200 mV. Both absolute redox potential values and their diurnal variations were depth-dependent. Because single redox measurements are insufficient in describing redox conditions in some soil systems, Hypnos can be a powerful tool when studying the effects of fluctuating redox conditions on metal availability and pollutant degradation.

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Copyright © 2004. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyASA, CSSA, SSSA